Question: Which of these numbers is prime? ${25,\ 33,\ 46,\ 73,\ 93}$
Answer: A prime number has exactly two factors: 1 and itself. The factors of 25 are 1, 5, and 25. The factors of 33 are 1, 3, 11, and 33. The factors of 46 are 1, 2, 23, and 46. The factors of 73 are 1 and 73. The factors of 93 are 1, 3, 31, and 93. Thus, 73 is a prime number.